Thoughts on ecology and the intersection of science and the humanities from the western hills of Oregon

Search This Blog

Loading...

Wednesday, April 17, 2013

The Natural History of Skunk Stink

I never knew that fresh skunk spray smells exactly like burning rubber.

Instead, as my dog leaped into the back porch after his brief pre-dawn potty break in the yard, I thought it was just some new form of particularly odious flatulence. This dog often has gas, and I had not yet had coffee. However, as I bent down to wipe his feet and the odor increased sharply in its intensity, I realized that my dog wasn't directly responsible for the stench. He seemed unconcerned, but he loves stinky odors, and the spray had missed his face.

There had been strong sulfurous fumes in the back yard for the previous week. It was almost March, and the skunks were stirring, looking for food and for love after winter. They are not shy about wandering around outside our house, although because they are normally strictly nocturnal we almost never see them. Skunks will spray predators that threaten them, but a female skunk will also spray persistent males bent on mating if she's really just not in the mood. Skunks aim quite well, so I suspected that my dog had interrupted an unhappy love affair and been splattered by the consequences.

Striped skunk, Mephitis mephitis. Photo: NPS

Anal glands are used by many species of mammal as the creators of scent calling cards; when your dog sniffs around another dog's feces, she's most likely focused on the droplets of scent secretion that are released during defecation. Possums also use anal gland secretion as a method of self-defense, but only skunks have the ability to take aim and fire. Skunks' glands are quite large, over an inch or three centimeters long, and each of the pair is equipped with a nipple-like structure called a papilla that acts as a movable nozzle. The glands contract with enough force to send the oily ooze flying ten feet or 3 meters distance.

Skunks are born blind and helpless, but
their glands contain musk by the end of their first week, and they are
capable of spraying at the age of 17 days, more than two weeks before
their eyes open for the first time. Researchers found that young skunks
were more likely than adults to spray than to run, hide, or charge. I
found no reliable reports of how long it takes for a skunk to refill its
glands after a full discharge. Presumably it takes some energy and
time, because skunks give plenty of warning before firing, and don't
seem willing to use all of their supply in a single encounter unless they must.

Striped skunks. Image from http://wdfw.wa.gov/living/skunks.html

Elements of the chemical composition of the spray were described as early as
1862 by German chemists, and a fellow German named Dr. O. Low did his best to continue the inquiry during an expedition to Texas in 1872. Low commented on the abundant opportunity to
collect
skunks and their musk during his travels, but
his
companions objected so vigorously to the ensuing odor
that he
was forced to abandon his efforts. He was further stymied from studying
his few skimpy samples by colleagues and students in the college at
which he worked "when the whole college rose in revolt, shouting 'A
skunk, a skunk is here!' I had to abandon the investigation."

A more thorough treatment of the chemical elements of skunk spray was published in 1896 by Thomas Aldrich of Johns Hopkins University,
who managed to obtain the glands of a number of skunks collected in Maine.“I have been more fortunate than my predecessors in being surrounded by
those who, for the cause of science, would endure even the odor of a skunk in
close proximity,” Aldrich wrote.

Aldrich found that the fluid’s vapors were highly
flammable and gave off sulfur dioxide when burned.He also discovered that even humans can sense
the presence of these compounds at concentrations of ten parts per billion.
This is equivalent to tasting a pinch of salt distributed across one ton of potato chips.

Spotted skunk, Spirogale gracilis

Image from http://wdfw.wa.gov/living/skunks.html

The composition of the musk is astonishing.Over 150 compounds containing sulfur have been isolated.Even more interestingly, each species of
skunk has its own chemical signature. The striped skunk’s musk contains seven
major volatile compounds, including three thiols, three thioacetate derivatives, and an alkaloid compound, 2-methylquinoline,
which is also used in pharmaceuticals including anti-malarial drugs.

The recurring skunky smell of a previously
sprayed dog who seemed odor-free until the dry fur is dampened results from the reaction between water and one of the thioacetate derivatives
remaining in the fur, creating one of the more volatile and smelly thiol
compounds. I found nothing in the literature regarding that first stench of burning rubber, but the odor had morphed into the sickening, familiar sulfur smell by breakfast time. The highly volatile chemicals responsible for the first overwhelming impression must have already begun breaking down in the presence of water and oxygen in the air.

To get rid of the odor, the thiols need to be converted to other, less
objectionable chemicals.Exposure to
oxygen will lead to their conversion to sulfonic acids.Tomato juice or other acids do not accomplish this critical piece of chemistry,
although a properly prepared solution of hydrogen peroxide will do the
trick. Regarding the well-established folklore regarding tomato juice, the authors of the book Land Mammals of Oregon commented, "Don’t waste good tomato juice- add a little vodka and drink it; it won’t
reduce the odor, but the odor won’t bother you so much!”

I didn't have any tomato juice or vodka on hand, only a bottle of doggy shampoo. I went to work at once, and by dawn, the dog was still stinking with sulfur, but now had undertones of green tea and lavender. At least he was clean. Fortunately, olfactory fatigue had set in, and we stopped noticing the stench unless we left the house for a while.

I'm not sure my dog has learned his lesson. I'll pay more attention to the atmosphere of early morning next year, making sure that no bad love is in the air before flinging open the door. Or at least, I'll make coffee first.

3 comments:

Hello, I just discovered your blog and enjoyed this post and the one about the possum. I look forward to reading your older posts, too. I'm an animal behaviorist who has an independent turtle cognition lab near Portland.

The smell of skunk spray is one that I will never forget. Odious flatulence is an understatement. It's more like toxic waste in the form of a vapor. I am an animal lover, and think that skunks are adorable, from far away. Also, the smell is something that no one should have to experience. http://360wildlife.com/services/skunk-removal-toronto/